1. Field of the Invention
The present invention generally relates to the operation of hybrid vehicles powered both by electricity from rechargeable batteries and by consumable fuel powered means, such as an internal combustion engine or a fuel cell, and, more particularly, to optimizing the cost of operating such a hybrid vehicle, especially when the cost of recharging batteries from external electric power sources may be less than the cost of recharging batteries from the onboard consumable fuel powered means. To this end, the present invention enables maximization of the use of electricity from external electric power sources and minimization of the use of electricity produced by the hybrid vehicle's onboard consumable fuel powered means, when the cost of recharging batteries from external electric power sources is less than the cost of recharging batteries from the onboard consumable fuel powered means.
2. Background Description
Hybrid vehicles, which use a combination of consumable fuel (such as gasoline, natural gas, hydrogen, and others) and battery-stored electricity are becoming a major segment of the automobile market. Such hybrid vehicles are displacing electric-only vehicles, as well as conventional vehicles powered solely by internal combustion engines or other consumable fuel powered means.
The electric power system of a prior-art electric-only vehicle is open, in the sense that such a vehicle lacks an onboard means to recharge the battery and therefore must be recharged from an external source. By contrast, the electrical power system of a prior-art hybrid vehicle is closed, in the sense that such a vehicle is not recharged from external sources but is instead recharged from an onboard consumable fuel powered means, which may be an internal combustion engine (powered by gasoline, diesel, ethanol, natural gas, hydrogen or another combustible fuel) or which may be a hydrogen fuel cell or other alternative consumable-fuel-based power unit.
Prior-art electric-only vehicles thus employ an open system in which batteries are recharged from an external electric power source, which may be conventional house current, a publicly accessible recharging facility, or any external source of electric power compatible with the vehicle's recharging system. Recharging such an electric-only vehicle from conventional house current alone may limit the useful range of the vehicle to no more than the distance that can be traveled on a single battery charge per round trip. External electric power sources for recharging electric-only vehicles could be provided at publicly accessible facilities; however, such facilities have, to date, not become widely available.
Prior-art hybrid vehicles employ a closed system in which the vehicle power system incorporates both a battery powered electric motor and a consumable fuel powered means from which the battery may be recharged. Power may be provided to the vehicle drive system by the electric motor and/or the consumable fuel powered means. Hybrid vehicles can refuel using consumable fuels, including but not limited to fuels which may be available from filling stations, without regard to availability of an external electric power source suitable for recharging. Access to an external electric power source is not required for recharging a hybrid vehicle, because a hybrid vehicle's batteries are recharged from the vehicle's onboard consumable fuel powered means.
A problem confronting prior-art hybrid vehicles is that recharging from the vehicle's onboard consumable fuel powered means makes the cost of recharging directly proportional to the cost of consumable fuel. That problem does not present itself with prior-art electric-only vehicles, where batteries are recharged from an external electric power source. As noted above, however, such electric-only vehicles may be less practical in that their range is limited when external electric power sources are not available for recharging along the route of travel.
The present invention thus relates to plug-in hybrid electric vehicles, which differ from conventional hybrid vehicles in that a plug-in hybrid electric vehicle has the ability to recharge its batteries either from a source outside the vehicle (such as by way of an electric plug) or from an onboard means (such as an engine or other consumable fuel powered means), whereas a conventional hybrid vehicle can be recharged only from its onboard engine. Plug-in hybrid electric vehicles thus combine the ability of prior-art electric-only vehicles to recharge from an external electric power source using electric power generated by any cost-effective means available with the ability of prior-art hybrid vehicles to recharge from the onboard consumable fuel powered means. The present invention accomplishes this in a manner that takes into account the fact that there may be times when the cost of recharging from the onboard consumable fuel powered means is not greater than the cost of recharging from an external electric power source, at which times it may be preferable not to recharge from an external electric power source.
Merely adding a capability to recharge a prior-art hybrid vehicle from an external electric power source, like an electric-only vehicle, would be inadequate, because it would not ensure an optimally cost-effective allocation between recharging from external electric power sources and recharging from the onboard consumable fuel powered means. In addition, there may be circumstances in which taking a detour in excess of a certain distance, solely for the purpose of recharging from an external electric power source, would be less cost-effective than relying on an onboard consumable fuel powered means for a complete or partial charge to extend the vehicle's range to reach an external electric power source closer to the route.
As a result, the present invention is directed to minimizing a plug-in hybrid electric vehicle's energy cost when the cost of recharging from external electric power sources is less than the cost of recharging from the onboard consumable fuel powered means. As noted, when energy from external electric power sources is less costly than energy produced by consumable fuel powered means, reliance solely on the onboard consumable fuel powered means may sacrifice cost-effectiveness. At the same time, reliance solely on external electric power sources may sacrifice practicality or range when availability of external electric power sources is not adequate for recharging en route.
The complexity of addressing such problems is increased by the fact that, in some embodiments, solutions change as the vehicle changes its position relative to available external electric power sources, which is something a vehicle necessarily does when it is put to its intended use of moving from place to place.